Many existing applications, such as in-the-ear (ITE), in-the-channel (ITC), or completely-in-the-channel (CIC) housings for hearing aids and personal communication devices (mobile phones or headsets) require the reproduction of one-of-a-kind parts of complex geometry. In these applications, the parts are unique and require a highly precise fit of the replacement part Sub-millimetre precision is for example required for ITE, ITC or CIC hearing aid housings; the housing Will otherwise cause inconvenience feedback, as well as irritation and possibly infection to the epidermis of the ear canal.
Existing methods to model and manufacture customised housings for hearing aids are very long and tedious processes. They introduce a great deal of uncertainty about the quality of the finished product. The process typically implies the creation of an impression of the user's ear canal. This impression must be adjusted manually and a mould replicating the user's meatus is created from the impression, either in plaster, gel, or silicone resin. A polymerisable liquid synthetic resin is produced, poured into the mould and polymerised at least partially. If the desired product is a shell for an individually fitted hearing aid housing, most of the liquid synthetic resin must be poured out of the mould again, before it completely polymerises. The resulting shell is ground to the desired size and appearance. The components must then be fitted manually into the shell; this operation is often problem-prone, since the shell has been designed without taking proper account of the components' shape and size.